Rapid transit or commuter type railway vehicles may be provided with either a fluid pressure operable brake system only or a combined electro-pneumatic brake system. The electro-pneumatic system may include a blending feature, that is, if the dynamic braking force diminishes or is insufficient for maintaining the braking level called for by the operator's signal, the pneumatic brake automatically blends in to supplement the dynamic brake to the extent necessary for maintaining the braking level desired. In some instances cars with both types of brake systems may be used in the same train in which event certain problems become manifest. For example, when a brake application is initiated on a train made up of cars equipped with both the combined electro-pneumatic system and the pneumatic system only, the dynamic brake, as is well known, reacts to the application signal first and, therefore, applies ahead of the pneumatic brake. The lag of the pneumatic brake application relative to the dynamic brake application presents no problem so long as all the cars in the train are equipped with similar type brake systems, that is, the electro-pneumatic system. But if the train includes some cars with the pneumatic brake system only, those cars with the electro-pneumatic systems get some braking action from the dynamic brakes thereon before any braking effect occurs on those cars equipped with pneumatic brakes only. Thus, when the pneumatic brakes do apply, such application lags the dynamic application, which occurs on certain cars only, the result being a push-pull effect on the train to thereby cause some discomfort to the passengers. In other words, at the onset of initial braking, the brake forces acting on the several cars are not compatible relative to time of application and, therefore, result in an unbalanced state.
Delay circuits have been incorporated in the signal circuits of the dynamic brake portion to attempt to delay the effectiveness of the dynamic brake until the pneumatic portion is actuated. But since the lag interval varies according to the degree of braking level signalled, it becomes inpractical to provide a lag circuit that would cover all situations.
The presently known electro-pneumatic brake system above discussed may also include monitoring means connected in parallel relation to the dynamic brake portion and the pneumatic brake portion for indicating that either the dynamic brake or the pneumatic brake, or both, are in effect. But, in that the respective braking forces of the dynamic and pneumatic brakes are recorded separately, the monitoring device does not give an indication of the total braking force of dynamic and pneumatic brakes prevailing at any given time, because they are not compared or related in the monitoring device, and, therefore, the information indicated may be inaccurate or misleading.